Negative childhood beliefs tend to stick around into adulthood is because our brains tend to be able to recall only information or memories that fit with our current belief system. This is confirmation bias.
If I already believe that I am a worthless person due to my childhood, then my brain is going to accumulate and look for evidence that I am worthless.
At the same time, my brain is going to ignore or minimize information and experiences that go against this belief. If I get a promotion, it’s simply because no one else wanted it. If I find a partner, it’s because they are too good and kind and don’t really see how terrible I am.
This is important to understand so that we can grant ourselves some grace in knowing why it is so hard to change our beliefs.
It is also important so that we can practice actively looking for disconfirming data. This can help provide a more balance and accurate view of ourselves over time.